Area Forecast Discussion
Issued by NWS Honolulu, HI

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000
FXHW60 PHFO 310147
AFDHFO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HONOLULU HI
350 PM HST SAT AUG 30 2014

.SYNOPSIS...
LIGHT TRADE WINDS WILL PREVAIL THROUGH THE HOLIDAY WEEKEND...
DELIVERING A FEW CLOUDS AND SHOWERS TO WINDWARD AREAS...MAINLY
DURING NIGHTS AND MORNINGS. THE LIGHT WINDS WILL ALSO ALLOW
AFTERNOON SEA BREEZES TO PRODUCE LOCALIZED CLOUD BUILDUPS AND A FEW
SHOWERS OVER LEEWARD AND INTERIOR AREAS. A MORE TYPICAL TRADE WIND
WEATHER PATTERN IS EXPECTED BY THE MIDDLE OF NEXT WEEK.

&&

.DISCUSSION...
CURRENTLY...ALTHOUGH LIGHT ENE TRADE WINDS PREVAIL ON THE LARGE
SCALE...WINDS ARE LOCALLY GUSTY THIS AFTERNOON AS DAYTIME HEATING
HELPS TO MIX HIGHER MOMENTUM AIR DOWN TO THE SURFACE. THE TRADES ARE
BEING SUPPORTED BY A RELATIVELY WEAK 1025 MB SURFACE HIGH CENTERED
ABOUT 1300 MILES N OF THE ISLANDS. HOWEVER...A WEAK AREA OF LOW
PRESSURE...MARKING THE REMNANT OF WHAT ONCE WAS TROPICAL CYCLONE
LOWELL...IS LOCATED ABOUT 700 MILES N OF THE ISLANDS NEAR 30N
155W...AND LIES BETWEEN THE HIGH AND THE ISLANDS. CLOSER TO HOME...A
POORLY DEFINED N-S ORIENTED TROUGH IS MOVING W ACROSS THE ISLAND
CHAIN...WITH THE AXIS CURRENTLY NEAR MOLOKAI. THE PRESENCE OF
THESE WEAK LOWS IS CONTRIBUTING TO THE RELATIVELY LOOSE PRESSURE
GRADIENT AND REDUCED TRADE WINDS NEAR THE ISLANDS. WHILE ONLY
LIMITED MOISTURE IS ASSOCIATED WITH THE PASSING TROUGH...IT APPEARS
THAT IT DID HELP TO FUEL CLOUDY SKIES OVER PORTIONS OF MAUI COUNTY
THIS AFTERNOON. AN OVERHEAD MID-LEVEL RIDGE IS MAINTAINING A STRONG
YET SOMEWHAT ELEVATED CAP ON THE ISLAND ATMOSPHERE...WITH AFTERNOON
SOUNDINGS INDICATING THE INVERSION BASE IS NEAR 10 KFT.

ALTHOUGH THE INVERSION BASE IS RELATIVELY HIGH...A RELATIVELY DRY
WEATHER PATTERN IS EXPECTED OVER THE NEXT COUPLE OF DAYS. THE
FORECAST CALLS FOR THE NEARBY TROUGH...AND THE LOWELL REMNANT...TO
MOVE GENERALLY WNW WHILE WEAKENING OVER THE NEXT DAY OR TWO...WITH
LOW LEVEL WINDS NEAR THE ISLANDS REMAINING LIGHT...BUT VEERING TO AN
ESE DIRECTION TONIGHT AND SUNDAY. THIS VEERING OF THE LOW LEVEL
WINDS WILL PLACE THE SMALLER ISLANDS IN THE WIND SHADOW OF THE BIG
ISLAND...AND WINDS ARE EXPECTED TO BE MORE VARIABLE IN DIRECTION ON
SUNDAY AS COMPARED TO TODAY. WHILE VOLCANIC EMISSIONS FROM THE BIG
ISLAND ARE NOT EXPECTED TO SPREAD OVER THE SMALLER ISLANDS WITH THIS
FLOW...SURFACE DEW POINTS ARE EXPECTED TO INCREASE SLIGHTLY...AND
WILL BE IN THE LOW 70/S STATEWIDE SUNDAY AND MONDAY. COMBINED WITH
THE LIGHT WINDS...CONDITIONS WILL BE WARM AND MUGGY.

ALTHOUGH THE WEAKENING REMNANT OF FORMER TROPICAL CYCLONE MARIE WILL
BE PASSING FAR NE OF THE ISLANDS DURING THE UPCOMING WEEK...FORECAST
MODELS DEPICT SUFFICIENT SURFACE RIDGING BUILDING N OF THE ISLANDS
TO SUPPORT A MODERATE TRADE WIND FLOW...INITIALLY STRENGTHENING AND
BACKING TO THE E ON MONDAY...BECOMING ENE TUESDAY...AND REMAINING
THAT WAY THROUGH THE END OF THE WEEK.

WHAT WE LIKE TO CALL A HYBRID TRADE WIND PATTERN IS EXPECTED
THROUGH THE REMAINDER OF THE HOLIDAY WEEKEND. IN THIS REGIME...
LIGHT TRADE WINDS MANAGE TO DELIVER A FEW SHOWERS TO WINDWARD
AREAS...MAINLY NIGHTS AND MORNINGS...WHILE WEATHER OVER LEEWARD
AREAS WILL BE DRIVEN BY THE DIURNAL CYCLE OF LAND AND SEA BREEZES.
THIS MEANS MOSTLY CLEAR NIGHTS AND MORNINGS...WITH INCREASING LATE
MORNING CLOUDS LEADING TO A FEW AFTERNOON SHOWERS THAT GRADUALLY
CLEAR IN THE EVENING. AS TRADE WINDS STRENGTHEN LATER IN THE
WEEK...LEEWARD AREAS WILL BE MOSTLY DRY...WITH BRIEF SHOWERS OVER
WINDWARD AREAS. THE EXCEPTION IS LEEWARD BIG ISLAND...WHERE CLOUDS
AND A FEW SHOWERS WILL FAVOR AFTERNOON AND EVENING HOURS BEFORE
CLEARING LATE AT NIGHT. MID-LEVEL RIDGING PERSISTING IN THE AREA
WILL KEEP THE ISLAND ATMOSPHERE STABLE...AND NO SIGNIFICANT MOISTURE
SOURCES ARE EXPECTED...THUS RAINFALL TOTALS WILL BE ON THE LOW END.

&&

.AVIATION...
VFR CONDITIONS PREVAIL AT ALL TAF SITES AND THESE CONDITIONS ARE
EXPECTED TO CONTINUE THROUGH THE EVENING AND ON THROUGH THE NIGHT.
SOME BRIEF MVFR CONDITIONS CAN BE EXPECTED OVER INTERIOR AND
MOUNTAIN AREAS THROUGH EARLY TONIGHT AS CLOUDS LEFTOVER FROM
DAYTIME HEATING LINGER ACROSS SOME AREAS.

WINDS WILL BE RATHER LIGHT OVER MOST AREAS THROUGH TONIGHT...WITH
LIGHT TRADES OVER THE ADJACENT COASTAL WATERS.

&&

.MARINE...
LATEST BUOY AND SURF OBSERVATIONS INDICATE A DECREASING TREND IN
SWELL/SURF HEIGHTS ALONG S FACING SHORES...AND THE HIGH SURF
ADVISORY FOR S FACING SHORES HAS BEEN CANCELLED. HOWEVER...SURF WILL
REMAIN ELEVATED ALONG S FACING SHORES FOR AT LEAST THE NEXT SEVERAL
DAYS. ALTHOUGH A REINFORCING SWELL IS EXPECTED SUNDAY...RESULTANT
SURF IS EXPECTED TO REMAIN BELOW ADVISORY LEVELS THROUGH MONDAY.
HOWEVER...A VERY LONG PERIOD /20-25 SECOND/ S SWELL ARRIVING TUESDAY
AND BUILDING THROUGH WEDNESDAY WILL LIKELY PRODUCE ADVISORY LEVEL
SURF INTO THURSDAY. LONG PERIOD SWELL FROM THE E IS STILL BEING
OBSERVED AT NEAR SHORE BUOYS...BUT THE MAGNITUDE OF THE SWELL IS LOW
ENOUGH THAT SURF ALONG E FACING SHORES IS BELOW ADVISORY LEVELS.

WINDS AND SEAS WILL REMAIN BELOW SMALL CRAFT ADVISORY THRESHOLDS FOR
AT LEAST THE NEXT SEVERAL DAYS...WITH AN OUTSIDE CHANCE THAT WINDY
MARINE ZONES AROUND THE MAUI AND THE BIG ISLAND REACH CRITERIA AS
TRADES INCREASE AROUND MID-WEEK.

&&

.HFO WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

DISCUSSION/MARINE...BIRCHARD
AVIATION...BURKE




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